Diesel engines become increasingly difficult to start as the temperature falls below freezing. It is not always convenient to keep the engine in a heated area or to raise the temperature of the engine with the use of engine block or oil heaters. The use of ether as a starting agent is dangerous because of engine pre-ignition and possible backfiring. When the engine is very cold and stiff, ether may not be effective at all.
Since the diesel engine typically has a battery-operated starter, there is the disadvantage that as the battery becomes colder, it loses efficiency. Thus, the starter turns the engine much more slowly than is desirable, and the compression strokes become so slow that much of the heat of compression is lost into the cold cylindar wall and piston. The resulting compressed air temperature is too low to ignite the injected diesel fuel. Even though glow-plug assisted diesel engines start easier than compression-start diesel engines, as the temperature continues to drop below freezing, the glow-plug assisted diesel will also fail to start at some subfreezing temperature. This is due to several factors such as the concentration of nitrogen in air inhibiting the oxidation of atomized fuel in the firing chamber and the poor atomization of low visiosity fuel at subfreezing temperatures.